1. Field of the Invention
The present invention relates to a fuel type identifying apparatus which identifies a type of a liquid fuel held in a fuel tank.
2. Description of Related Art
The structure of a conventional internal combustion engine and a combustion method in the engine depend on a type of a liquid fuel used in the engine. For example, in case of a gasoline engine, gasoline is used as a fuel, and the gasoline is mixed with air at the optimum ratio to obtain an air-fuel mixture. The air-fuel mixture is fed into a cylinder of the engine and is compressed in the cylinder. The compressed air-fuel mixture is ignited by using a spark plug, thereby being exploded. Further, in case of a diesel engine, light oil is used as a fuel, only air is initially fed and compressed into/in a cylinder of the engine, and then light oil is injected into the cylinder to explode a mixture of the air and light oil due to a self ignition. As another combustion method for the gasoline engine, similarly to the self ignition in the diesel engine, a technique of the self ignition applied to the gasoline engine has been researched to reduce a fuel consumption of the gasoline engine.
Further, a diesel engine using kerosene or vegetable oil as a fuel has been proposed. For example, Published Japanese Patent First Publication No. H09-158731 discloses this diesel engine. Particularly, because vegetable oil can be mass-produced due to biotechnology, a diesel engine using the vegetable oil is called a bio-diesel engine. In this bio-diesel engine, an exhaust gas can be reduced. Further, in consideration of exhaustion of the petroleum in the future, the spread of the bio-diesel engine has been expected.
Moreover, a multi-fuel engine operable by using any of a plurality of types of fuels has been proposed. In this engine, structural parts common to those of the conventional engine usable for only one type of fuel are used, so that the multi-fuel engine can be produced at low cost. Further, a user of this engine can freely select the fuel type, so that the user can reduce a cost of the fuel used for the engine.
However, in case of the engine operable by using any of the types of liquid fuels such as gasoline, diesel, vegetable oil and the like, operational conditions (for example, quantity of injected fuel, compression ratio in air-fuel mixture or air, valve timing and the like) optimum to the engine depend on the type of the fuel actually used for the engine. Therefore, it is required to change the operational conditions optimum to the engine for each fuel type so as to obtain fuel combustion conditions optimum to the type of the fuel actually used in the engine. Therefore, a fuel type identifying apparatus has been required to identify a type of a liquid fuel supplied to an engine.